There is a desire in the production of hydroformed tubular metal parts to be able to form a precise and accurate threaded hole in the hydroformed part. Without requiring that this be done as a secondary operation following removal of the part from the hydroforming dies as is presently done. Recognizing that if a required threaded hole could be made in an in-die procedure while the hydroformed part remains in the dies and without producing a slug or chips, there are considerable time and cost savings to be gained.
Moreover, it is known that required holes of various shapes can be pierced in the hydroformed part in a hydropiercing and extruding operation while the part remains in the dies under internal pressure and without producing a slug that could fall into the part and later have to be removed. So it would also be to considerable advantage if the formation of a required threaded hole in the part could be accomplished simultaneously therewith. Without either of these operations producing a slug or chips and thereby not require additional processing or cycle time or cleanup or a secondary operation.
There are of course a wide variety of thread cutting and thread forming taps for tapping a thread in a preformed hole in a part. With the advantage of the latter type of taps being to precisely and accurately form a stronger thread by displacing material without producing chips. However, conventional thread forming taps while not producing chips nevertheless still require that a hole first be formed in the part. Furthermore, the wall of the hydroformed parts is typically not thick enough to allow the number of threads necessary to securely hold a particular screw or bolt to the hydroformed part or to allow the use of self-tapping screws or bolts. And in that event, weld nuts are typically added in a secondary operation.